1. Field of the Invention
The present invention generally relates to methods of producing p-type CdSs and, more particularly, is directed to a method of producing a p-type CdS suitable for use in a light-emitting element such as a photoluminescence element, a laser diode or the like.
2. Description of the Prior Art
Recently, short-wavelength light sources have been demanded, for example, in optical recording and/or reproducing techniques due to the requirement for high-density recording and high-resolution.
In a CdS mixed crystal or CdS crystal in an intermixing state or disordered state which is a II-VI compound semiconductor, it is difficult to produce a p-type CdS mixed crystal.
According to the general semiconductor theory, acceptor and donor impurities to be doped in the II-VI mixed crystal are selected from I and VII elements, respectively. However, in the CdS mixed crystal, since the steam pressure of the element S is high, in the process of forming a p-type impurity doped CdS, the element S is likely released from the CdS to leave vacancies. Thus, the degree of crystallization of the CdS alloy becomes low.
Further, there has not been realized a p-type CdS whose acceptor level is low. This is because, even in the lower acceptor level elements utilized as impurities, for example, Li, Na and P, the acceptor levels thereof are 165 meV, 169 meV and 120 meV, respectively.
FIG. 1 shows an emission spectral distribution of a conventional CdS in which Na and Cl are doped as impurities. As clear from FIG. 1, the wavelengths of emission light of this CdS are not sufficiently short.
Accordingly, there has not been realized an acceptor-donor pair type light emitting element which utilizes the CdS mixed crystal and can emit light of short wavelengths.